Message numbering is an increasingly popular feature of radio messaging systems. This feature, which typically sends a two-digit message sequence number along with each message, is intended to increment the number by unity with each subsequent message. Thus, if a subscriber receives a message number that is more than a unity increment higher than the last received message, then the subscriber must have missed a message. In a system which offers message retrieval the subscriber can call in and retrieve the message associated with the missing message number.
Message numbering can degrade transmission efficiency, however, because to guarantee that the message number remains in sequence, each numbered message must be transmitted in the same order in which the message was received from the central control terminal which numbered the message. This implies that when forming a frame of data for transmission, the output controller cannot switch the order of numbered pages. On the other hand, for greatest transmission efficiency and highest system capacity the output controller must assemble the frame of data with messages that fill the frame as fully as possible. This implies a necessity for swapping messages that are too long to fit into the current frame, with shorter messages that can fit. In prior art systems, that has required switching the transmission order of the swapped messages, thereby confusing subscribers who use message numbering for detecting missed messages.
Thus, what is needed is a method and apparatus that dependably transmits message numbers in the proper sequence, while at the same time allowing optimal filling of each frame of data.